Insight into the corrosion behaviour of friction stir welded joints: A comparison between 6061-T6 and 7075-T651 aluminium alloy joints in aerated NaCl

This investigation analyses the corrosion behaviour of similar and dissimilar FSW joints produced from the Al alloys AA6061-T6 and AA7075-T651. Potentiodynamic polarization tests in an aerated marine (3.5% NaCl) environment confirmed that FSW deteriorates corrosion resistance, decreasing in the order: AA6061BM > AA7075BM > AA6061 joint > AA6061/AA7075 joint > AA7075 joint. The complementary analyses such as tensile tests, SEM, EDS, and XRD were employed to correlate microstructural heterogeneities with corrosion behaviour and tensile strength. In each instance, the NZ exhibited the highest corrosion rate, indicating a pronounced anodic nature. The enhanced galvanic corrosion at the NZ was attributed to the fine recrystallized grains, and the morphology and distribution of Si-, Zn-, Cu-, Fe-rich IMCs. Among the joints, AA6061/AA6061 displayed superior resistance to corrosion (-712.6 mV SCE , 609.75 μm/y) due to the presence of Mg 2 Si and a lower amount of Cu-rich IMCs on fairly coarse recrystallized grains (15.8±0.4 µm). The dissimilar AA6061/AA7075 joint demonstrated ~3.1 times better corrosion performance than the AA7075 joint, possibly due to the positive effects of intermediate grain size (~5-12 µm) and Si-rich remnants that may have suppressed MgZn 2 reactivity. Corrosion attacks predominantly manifested as pitting, exfoliation, and IGC, while corrosion products Al 2 O 3 , AlOOH, Al(OH) 3 acted as the main passivation barrier.